The proposed study involves three phases. The primary phase will be to develop a sensitive methodology for assessing the abuse liability of stimulant and sedative drugs, using recreational users of such drugs as subjects. Safe euphoriant doses of a standard stimulant (d-amphetamine) and a sedative (methaqualone) will be established in informal living room-like situations in order to encourage drug responses which are the closest approximation of "naturally" occurring ones. These initial drug studies will establish standards against which other drugs may be compared. It is believed that this approach offers a number of advantages over currently used prisoner volunteer and human operant drug-seeking behavior studies. The second phase will apply the methodology to assess the abuse liability of both stimulant and sedative drugs with known or presumed abuse liability (e.g., fenfluramine, mazindol, magnesium pemoline, diazepam, propranolol and lorazepam) and of recent drugs of unknown abuse liability. Global ratings of effect, discrete self-reports of mood states and subjective experience, and observations of group interactions will measure subjects' responses to standard and test drugs. The third phase is to establish an ongoing unit capable of performing prompt abuse liability assessments on new drugs before they are approved for distribution or in situations where need for such assessments of marketed drugs becomes important.